1. Field of the Invention
The present invention relates to a scroll compressor for use in an air conditioner.
2. Description of Related Art
In general, when a room air conditioner is used for both heating and cooling purposes, the evaporation temperature and condensation temperature to be set change variously. Where a scroll compressor, which is obliged to take a certain volume ratio for structural reasons, is employed in the room air conditioner, it is considerably difficult to select the volume ratio of the scroll compressor. Accordingly, a relatively large volume ratio has been hitherto selected in order to ensure the performance of the scroll compressor in any working range.
However, when a scroll compressor having a large volume ratio is operated at a relatively low cooling or heating load, the scroll compressor is considerably reduced in efficiency due to excessive compression peculiar thereto. In contrast, when a scroll compressor having a very small volume ratio is operated at a relatively high load, insufficient compression is caused, resulting in a considerable reduction in efficiency.
To overcome this problem, Japanese Laid-Open Patent. Publication (unexamined) No. 61-14492 discloses a scroll compressor with a discharge valve wherein the volume ratio is set to be smaller tan that determined by the condensation temperature and evaporation temperature during a heat pump cycle.
However, this compressor has the following drawbacks. The volume ratio determined by the evaporation temperature and condensation temperature used during the actual heating operation is relatively small and, hence, insufficient compression is brought about for almost the whole operating time, which in turn causes a back flow of the discharge gas, thus considerably reducing the compressor efficiency.
Although the discharge valve is provided so as to reduce the back flow, if a spring constant thereof is set large to close it quickly, another problem, e.g., an increase of noise or the like is generated. In contrast, if the spring constant is too small, the effect of the discharge valve cannot be expected.
It is therefore difficult to reduce the annual consumption of power required for the operation of the air conditioner.
In order to enhance the reliability of the compressor, it has been also proposed to provide a compliance mechanism in the axial direction, with a tip seal mounted on only an orbiting scroll. In this case, for the purpose of minimizing inclination of the orbiting scroll which has been hitherto caused by an overturning moment specific to the scroll compressor, if the orbiting scroll is physically pressed strongly against a stationary scroll, the compressor efficiency is reduced considerably. If the force or pressure is small, the effect is reduced. It is therefore necessary to pay scrupulous attention to both the magnitude of the force or pressure and sufficient sealing so as not to reduce the compressor efficiency.
Especially, if a horizontally arranged scroll compressor is operated at high speeds, it is preferred that a crank shaft be sufficiently supported at opposite ends thereof. Moreover, an oil feed means should be provided to surely supply a lubricating oil to each bearing, resulting in an increase in manufacturing costs.
At the same time, the horizontally arranged scroll compressor is required to support an axial force acting on the crank shaft, which likewise increases costs as a result of an increase in the number of elements.